The present invention relates to a liquid crystal display apparatus suitable for a motion picture display, such as a television picture display.
Various liquid crystal materials have been used for liquid crystal display apparatus, such as nematic liquid crystal, smectic liquid crystal and polymer dispersion liquid crystal.
A TN (twisted nematic)-mode liquid crystal device using a nematic liquid crystal among these liquid crystals requires a long response time of 50 to several hundred ms (milli-second) in a halftone display, so that the response is not completed within one frame period (e.g., 16.7 ms at 60 Hz) and a motion picture is sometimes blurred because of image flow, thus providing an inferior xe2x80x9csharpness of motion picturexe2x80x9d to be unsuitable for a motion picture display such as television picture display.
On the other hand, a liquid crystal device using a smectic liquid crystal having a spontaneous polarization and an OCB (optically compensated bend)-mode liquid crystal device utilizing a bend alignment state of a nematic liquid crystal exhibit a response time which is one tenth to one thousandth as short as that of the conventional TN-mode liquid crystal device, thus being able to complete a response within one frame period and therefore expected to be suitable for motion picture display.
In recent years, however, it has been found that a short response time alone is not sufficient for providing xe2x80x9csharpness of motion picturexe2x80x9d. As described in H. Ishiguro et al., xe2x80x9cConsideration on Motion Picture Quality of the Hold Type Display with an octuple-rate CRTxe2x80x9d, Technical Report of IEICE (Institute of Electronics Information And Communication Engineers, Japan), EID 9-64 (1996-06) pp. 19-26, a continuous lighting-type display apparatus (hereinafter referred to as xe2x80x9chold-type display apparatusxe2x80x9d) like a conventional liquid crystal display is in principle inferior in motion picture quality compared with a pulse lighting-type display apparatus (hereinafter called a non-hold-type display apparatus) such as a CRT (cathode ray tube). Accordingly, as described in the paper, it has been known that the motion picture quality of a hold-type display apparatus wherein a picture is ordinarily displayed continually over one frame period, can be improved by placing a portion of the period in a non-display state. Further, the picture quality can be improved at a high picture display frequency of, e.g., 120 Hz, higher than 60 Hz.
According to our study, however, even when a hold-type display apparatus is operated in a substantially non-hold type display mode by placing a non-display period, there has been found a problem that the motion picture quality can be deteriorated at different levels depending oh the responsiveness of the liquid crystal and the back light source. Further, it has been also found that the motion picture quality is also affected by other factors, such as the pixel size, luminance and contrast of the display apparatus.
In view of the above-mentioned problems, a principal object of the present invention is to provide a liquid crystal display apparatus with an improved motion picture quality.
A more specific object of the present invention is to provide a liquid crystal display apparatus with a motion picture quality improved depending on the responsiveness (response time) of the liquid crystal.
Another object of the present invention is to provide a liquid crystal display apparatus with a motion picture quality improved depending on the pixel size, luminance and contrast of the liquid crystal device.
According to the present invention, there is provided a liquid crystal display apparatus, comprising:
a liquid crystal device including a pair of substrates and a layer of liquid crystal disposed between the substrates so as-to form a matrix of pixels, and
drive means for driving each pixel in a succession of frame periods each having a duration of Fr and divided into a first period and a second period in succession so as to display a first luminance in the first period and a second luminance below the first luminance in the second period under a condition satisfying: Tap+(xcfx84offxe2x88x92xcfx84on)/2Fr=Tsxe2x89xa60.6, wherein Tap represents a time aperture ratio determined as a ratio between the first period and one frame period Fr, xcfx84on represents a rise time required for a luminance change of from 0% to 90% during a switching from 0%-luminance to 100%-luminance, and xcfx84off represents a fall time required for a luminance change of from 100% to 10% during switching from 100%-luminance to 0%-luminance based on a normalized luminance scale with 100% at a maximum luminance and 0% at a minimum luminance of each pixel.
According to another aspect of the present invention, there is provided a liquid crystal display apparatus, comprising:
a liquid crystal device including a pair of substrates and a layer of liquid crystal disposed between the substrates so as to form a matrix of pixels, and
drive means for driving each pixel in a succession of frame periods each having a duration of Fr and divided into a first period and a second period in succession so as to display a first luminance in the first period and a second luminance below the first luminance in the second period under condition satisfying: Tap+xcfx84off/2Fr=Tsxe2x89xa60.65, wherein Tap represents a time aperture ratio determined as a ratio between the first period and one frame period Fr, "sgr"off represents a fall time required for a luminance change of from 100% to 10% during switching from 100%-luminance to 0%-luminance based on a normalized luminance scale with 100% at a maximum luminance and 0% at a minimum luminance of each pixel.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.